In recent years, hydrogen fuel cells are being put into practical use, giving rise to demand for gas sensors that detect hydrogen. Hydrogen is detected by a catalytic combustion gas sensor. This sensor uses a resistor holding a catalyst containing platinum, palladium, or rhodium, for example, which causes hydrogen to combust, on a metal wire formed from a metal such as platinum or palladium or an alloy thereof. The catalytic combustion gas sensor detects hydrogen using changes in the resistance value of the resistor, which occur when the hydrogen burns and the temperature rises.
Such gas sensors are sometimes used even in subzero environments. When a gas sensor is used in a subzero environment, water produced when hydrogen and oxygen combust freezes and forms frost around the gas sensor. In a case where the frost reaches the resistor, the frost will inhibit the diffusion of hydrogen and worsen the hydrogen detection accuracy. Accordingly, the gas detector disclosed in Patent Document 1 (JP 5927647 B) is configured such that a support part supporting a noble metal wire penetrates a circuit board, and a heating unit that heats the support part is provided on the side of the circuit board opposite from the side on which a housing containing a gas detection sensor is located.